function make_person_object(firstname, lastname, age) {
    this.firstname = firstname;
    this.lastname = lastname;
    this.age = age;
    // Note, we did not include a return statement
}

var John = new make_person_object("John", "Smith", 45);
console.log(John); // {firstname: "John", lastname: "Smith", age: 45}

make_person_object.prototype.full_name = "N/A";
make_person_object.prototype.greet = function(){ 
    console.log("Hello! I'm", this.full_name, "Call me", this.firstname); 
};

console.log(John.full_name);